Which area of the heart is primarily responsible for beginning the electrical conduction system?
AV node
Purkinje fibers
SA node
Bundle of His
The Correct Answer is C
A. AV node:
The AV node serves as a secondary pacemaker and delays the conduction of impulses from the atria to the ventricles, allowing ventricular filling. It does not initiate the heartbeat under normal conditions.
B. Purkinje fibers:
Purkinje fibers distribute impulses rapidly throughout the ventricles but act as a backup pacemaker at 20-40 bpm if higher centers fail. They do not initiate the cardiac rhythm.
C. SA node:
The SA node, located in the right atrium near the superior vena cava, is the primary pacemaker of the heart. It generates impulses at 60-100 bpm, initiating atrial contraction and setting the overall heart rate. Dysfunction of the SA node leads to arrhythmias such as sick sinus syndrome.
D. Bundle of His:
The Bundle of His conducts impulses from the AV node to the ventricles but is not a primary pacemaker. Its rate is slower than the SA node and primarily ensures coordinated ventricular contraction.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Cardiac output remains unchanged as the heart compensates:
The heart has limited compensatory capacity. A significant LAD blockage reduces perfusion to the anterior wall and interventricular septum, impairing left ventricular contraction and reducing output.
B. There is decreased cardiac output due to impaired left ventricular function:
LAD blockage leads to ischemia of the left ventricle, reducing stroke volume and cardiac output. This can result in heart failure or cardiogenic shock if severe.
C. There is increased cardiac output due to compensatory mechanisms:
Compensatory mechanisms like increased heart rate may temporarily support output, but overall cardiac output declines due to impaired contractility.
D. Cardiac output increases initially, then decreases:
While compensatory mechanisms may attempt to maintain output, in acute LAD blockage, immediate decline in contractility dominates; initial increase is not typical.
Correct Answer is A
Explanation
A. Supplies the lateral wall of the left ventricle:
The circumflex artery branches from the left coronary artery and supplies the lateral and posterior walls of the left ventricle as well as part of the left atrium. This supply is crucial for maintaining effective left ventricular contraction and overall cardiac output.
B. Supplies the right ventricle:
The right ventricle is primarily supplied by the right coronary artery, not the circumflex artery. Misidentifying this can affect understanding of infarct locations.
C. Supplies the interventricular septum:
The interventricular septum is mainly supplied by the LAD artery, which is critical for coordinating left ventricular contraction.
D. Supplies the right atrium:
The right atrium is primarily supplied by the RCA, not the circumflex artery. Understanding arterial supply is important for predicting conduction system involvement in MI.
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